As is known, a gas turbine for aeronautic engines generally comprises a number of rotating bladed sectors, each of which, in turn, comprises a turbine disk connected to adjacent turbine disks and carrying a coupled blade crown.
As is also known, turbine disks are components that are subjected to high stress, both mechanical, due to the effect of centrifugal components and, above all, thermal, since they operate in an extremely high temperature environment due to close vicinity with the flow of hot gases that impact the blades. For optimal turbine operation it therefore becomes necessary to control the operating temperature of these disks, maintaining the operating temperature below a set or critical threshold value.
To that end, it is known to send to each of the turbine disks its own cooling airflow, separate from the other cooling airflows. Each cooling airflow is normally formed by bleeding a predetermined quantity of air from the compressor and conveying the bled air to the area of connection of the blades to the respective turbine disk. In the area of connection of the blades to the disk, the air is made to flow through passages, each one being defined on one side by a slot in the turbine disk to be cooled and by the leading portion or lobe of the relevant blade, on the other. While traversing the passages, the cooling air progressively heats up, carrying away heat by convection; at the exit, the heated air is first fed into a mixing chamber where it mixes with part of the mentioned flow of hot gases, forming a mixture of lower temperature that passes over the side walls of the blade and the turbine disk, after which the same mixture is reinserted in the flow of hot gases before this flow passes over the bladed sector arranged downstream of the cooled turbine disk.
Although it is used, for various reasons, the described cooling method is found to be less than satisfactory.
First of all, cooling of the disks is performed in conditions of low efficiency and therefore the cooling capacity of the incoming air is only exploited in part. In consequence, the air exiting from the respective turbine disks has a relatively low temperature for which, when mixed with the hot gases entering the downstream stage, it significantly lowers the temperature of the hot gases in an undesired manner.
With bleeding being carried out for each turbine disk, as the number of turbine disks increases, so does the quantity of air that is used and the overall efficiency consequently decreases.